The long-term goal of this project are: (1) to gain an increased understanding of the correlations between biomechanical and functional measures of motor control changes in a population of ambulatory elderly, and (2) to establish the scientific foundation fir abn intervention program that could be used to improve motor control in older adults and thereby serve to reduce the incidence of falls in the elderly. Our previous studies suggest that there are significant abnormalities in postural sway and gait initiation in elderly people, that may predispose these individuals to fall. In fact, in one pilot study, we found that elders at risk of falling had exaggerated impairments in postural sway. We also have preliminary evidence indicating that the abnormalities in postural sway and gait initiation are both associated with increased lower-limb muscle activity. It is now known, however, whether these abnormalities have functional consequences such as balance impairment and falls. In addition, it is not known whether reducing lower-limb muscle activity via EMG biofeedback improves or worsens balance function and gait initiation in elderly people. Therefore, the specific aims of this study are: (1) to determine the relationships between lower-limb muscle activity and (a) postural sway dynamics and balance function, and (b) gait-initiation dynamics and mobility function, in ambulatory elderly people; (2) to determine cross-sectionally whether variations in postural sway dynamics and gait initiation in elderly people are associated with falls; and (3) to determine whether reducing lower-limb muscle activity via EMG biofeedback improves or worsens balance function and gait initiation in elderly people. We plan to study two samples of healthy ambulatory elders: one sample of 100 fallers with unexplained falls and one sample of 100 non-fallers. Quiet-standing and gait- initiation tests (with and without EMG biofeedback) will be conducted on each subject. This work could serve to reduce significantly the frequency, morbidity and cost of falling and assist aged individuals in achieving maximal independence in activities of daily living and mobility.